Experimental Challenges at EUPHORE: The NOx Denuder

Solution

Shar Samy

April 9, 2007

Presentation Outline

• European Photoreactor (EUPHORE)– Overall description– Technical Specifications

• Atmospheric Transformation of Diesel Emissions

-Objectives

-Experimental challenges, in regards to NOx

-Attempted solutions, and results

The chambers in Valencia, Spain.

Technical Specifications

• half-spherical Teflon (FEP) bag with a volume of about 200 m3

• fluorine-ethene-propene (FEP) foilSpecifications: 0.13mm thickness, transmission >80% (280-640nm)

• chamber is self stabilizing against wind distortions when operated with an excess pressure of 100-200 Pa

• internal framework made of epoxy-resin tubes based on a half-spherical network construction keeps the foil in shape in the absence of excess internal pressure

• refrigeration system integrated in the chamber floor, which compensates for chamber air heating by solar radiation

• Ports for input of the reactants and sampling lines for the different analytical instruments are located on the chamber floor

Instrument Compounds / Parameter

Detection limit Sampling Method Analysis Type

FTIR Magna 550 VOCs 10 ppb In-situ White mirror system (553m optical path)

On-line

GC-FID/PIDFison 8000

VOCs,Carbonyls

20 ppb10 ppb

5 ml sampling loop On-line

Fison TGA GC/FID VOCs 1 ppb Cryogenic enrichment On-line

HPLC –UV/VIS Carbonyl Compounds 1-2 ppb by DNPH

DNPH cartridges30 l air samples

Off-line

HPLC -Fluorescence H2O2, Hydroperoxides < 1 ppb Double stripping coil Off-line

NOx Monitor

ECO Physics

NO, NO2 < 1ppb Teflon line On-line

NOx Monitor Labs. NO, NOy 1 ppb Teflon line On –line

CO Monitor TE48C CO 20 ppb Teflon line On line

Ozone Monitor O3 1 ppb Teflon line On-line

Spectral Radiometer Solar Flux ------ Inside the reactor, 50 cm above the ground

6 min average

Temperature T ------ Below fan in the shadow 1 min average

Pressure P ------ Teflon line 1 min average

Dew Point TS-2 Humidity -50ºC Teflon line 1 min average

Chamber B, Analytical Instrumentation

Room for air purification and chamber floor cooling systems

Engine test rig

Exhaust gas inlet system

Smog chamber laboratory

EUPHORE chamber

Heated tube

The overall objective of this study is to investigate photochemical

transformations of diesel emissions in the atmosphere.

The specific aims are:

(1) to characterize the gas- and particle- phase products of atmospheric transformations of diesel emissions under the influence of

sunlight, ozone, hydroxyl radicals, and nitrate radicals (in the dark).

(2) to explore the changes in biological activity of diesel exhaust before and after the atmospheric transformations take place.

Why is all this work necessary ?

We all understand part of the complexity

• Once released into the atmosphere, primary diesel emissions (or any other direct emissions) are subject to dispersion and transport .

• Various physical and chemical processes, determine their ultimate environmental fate.

• The role of the atmosphere may be compared in some ways with that of a giant chemical reactor in which materials of varying reactivity are mixed together, subjected to chemical and/or physical processes, and finally removed.

The Photoreactor Model

WHY?

• better understanding of the health risks of exposure of general populations to secondary pollutants derived from atmospheric transformation of diesel emissions.

• geographic extent of the influence of these emissions (coupled with future sampling campaigns), “Transformation Profile”

Experimental Challenges

The modern 1.8 L, Lynx V277 90PS Stage 3, Delphi Fuel System, Fixed Geometry Turbo Diesel Engine emits very high levels of NO + NO2 = NOx

~400ppm !

This engine is used in the Ford Focus and Transit Connect automobiles.

Experimental Matrix(three campaigns combined)

Run Description Purpose # of Runs Run Description Purpose # of Runs

Diesel Exhaust Dark (D-1)

Determine changes in exhaust composition due to aging in chamber.

8 Diesel Exhaust Only,

Light (L-1)

Examine effects of photolysis reactions on exhaust composition, low NOx

4

N2O5 + Diesel

Exhaust,Dark (D-2)

Investigate effects of NO3 on

diesel exhaust composition. N2O5

decomposes to form NO2 and NO3.

8 HCHO + Diesel Exhaust, Light(L-2)

Study reactions of OH radicals (from HCHO photolysis) with diesel exhaust under low NOx

6

O3+Diesel

Exhaust,Dark (D-3)

Study reactions of ozone with diesel exhaust in the dark, under low NOx

3 Diesel Exhaust + Toluene, Light(L-3)

Diesel exhaust as seed aerosol during the oxidation of toluene. Low NOx conditions

4

Objective

• Investigation of atmospheric transformation processes under realistic ambient conditions?

• In order to carry out light exposures and O3 dark exposures in low NOx conditions, a NOx denuder was developed for this work.

What is a NOx Diffusion Denuder ?

• A device that removes gas phase NO + NO2 = NOx from an air or effluent stream, while allowing other gases and suspended particles to flow through unperturbed (ideal).

Isolation and Enrichment of Analytes, “Denudation”

• A dynamic method based on passing of an air (effluent) stream through a suitably built container in which certain components of the analyzed air sample are retained (enriched).

• Selective adsorption of NOx is achieved by way of diffusion or permeation.

Assuming movement of molecules and/or particles is achieved by two

main forces:

• A force vectored in accordance with the direction of the gas stream, resulting from the force flow of gas

• A force perpendicular to the longitudinal axis of the denuder (and its walls), resulting from the radial diffusion

From: Kloskowski, A. et al, Critical Rev. Analytical Chem. , 2002.

• Solid particles are relatively massive and travel straight through the denuder (high momentum)

• “The gas molecules are moving all over the place, like toddlers; eventually they hit the wall and stick. The trick is to calculate the airflow and the length of the tube -- to make it short enough so the particles stay airborne but long enough for the gas to get trapped." Lara Gundel, 1999

Diffusion Coefficients

• NO2, D=10 cm2/min

• Particles 1um D=1.64x10-5cm2/min

Some basic principles of operation

- flow of gas must be stable and laminar

- analyte releasing technique cannot influence sample composition

- the device should be operated under steady state conditions of pressure and temperature

- temperature and viscosity distributions must be uniform within the stream of gas

- longitudinal diffusion of the analyzed gaseous components should be negligibleas compared with the linear velocity of gas flow

- sorption material should be a good sink for the analytes in question

- adsorbate should not undergo any secondary transformations within the denuder, that is, neither new compounds should appear, or those already present disappear.

What is Laminar Flow?

Re = velocity*diameter*density viscosity

Re < 2000, indicates laminar flow

Reynolds numberA non-dimensional number, which is the ratio of inertial

forces to viscous forces

Commonly used to identify different flow regimes

(turbulent vs. laminar)

Cobalt Oxide

• An efficient absorption material for the capture of nitrogen oxides (NO, NO2, and HNO3) from exhaust streams

• Coatings can be regenerated by heating them in a flushing air or oxygen flow to about 400C, resulting in the release of absorbed NOx, thus allowing the material to be used again

Campaign #1January, 2005

• A small denuder was initially constructed (for the winter, 2005 campaign) using cobalt oxide coatings on the inner walls of small cylindrical stainless steel tubes, but found some objections to this design approach because of imperfect adhesion of the coating to the metal and the NOx removal efficiency

• A 2-min introduction of diesel exhaust to the chamber produced approximately 30 μg/m3 of diesel PM and nearly 1 ppm of NOx (30% of this as NO2)

• Because of the high NOx concentrations in the chamber, it was not possible to carry out certain exposure scenarios. For example, dark ozone exposures

Initial Denuder

FTIR Data Chamber

0

100

200

300

400

500

600

9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00

Time, hh:mm

NO

, NO

2 an

d N

Oy

Con

cent

ratio

n, p

pb

NOy ML

NO

NO API

NO ECO

NO2

NO2 API

NO2 ECO

12-Jan-2005BExhaust diesel (15% aromatics) with NOx denuder

Very little removal efficiency, immediate blow through of NOx is apparent

Campaign #2May, 2005

• Ceramic (e.g., “cordierite”) honeycomb denuder configuration

Pros and Cons

• Maximized surface area, which the honeycomb configuration provides is an attractive feature

• Stability of the cobalt oxide coating on the honeycomb sections resulted in frictional and turbulent material loss (flaking)

• Impaction of particles (d=0.48cm), and lack of removal efficiency (and storage capacity) of NOx

NO mixing ratio for honeycomb denuder experimental setup.

FTIR NO, May 2005

0

100

200

300

400

500

600

700

6 7 8 9 10 11 12 13 14 15 16 17 18 19

GMT Time (hh)

Co

nce

ntr

atio

n (

pp

b)

nitric oxide

Improvements Needed

• Work was carried out in fall/winter 2005-2006 to improve the design of the denuder. A design goal of 90% NOx absorption in concentrations ranging as high as 400ppm (typical for a modern diesel) was established at the onset of the work.

• A Cobalt Oxide coated NOx absorptive material (“GROG”, an industry term, a firebrick prerequisite material ) was developed

• A miniature multi-channel cylindrical denuder was utilized for testing

Cobalt Oxide Coated GROG

• GROG is composed of Silca (~50%), Alumina (~%40), Iron Oxide (~2%), Titania (~2%), and several other earth metals (sodium, potassium, etc…)

Pre-coated, sifted GROG

Post-coated, GROG

GROG coating procedure ? Make it up !

4-channel cylindrical denuder

• Each channel is 39cm long (four total), with a channel diameter of 2.5cm • An additional 15cm pre-chamber was constructed to establish laminar flow

of effluent, prior to the channel entrances

• Packing of absorbent material on the

outside of the main interior channels

allows for efficient transport and

replacement of the packing material

(or regeneration )

• Once effluent flow is established, gaseous diffusion through the mesh apertures (~1mm) allows for efficient

removal of NOx

Channel pathways were left

completely open (line-of-site), to

reduce particulate loss due to impaction

Mini-denuder setup

NO Denuder Experiment 10-26-05

y = 0.0166x2 - 0.8711x + 17.519

0

20

40

60

80

100

120

140

160

180

0 20 40 60 80 100 120 140

Elapsed Time (Minutes)

FT

IR R

ead

ing

, PP

M

NO removal efficiency remained >90% for approximately 80 minutes, utilizing a 400ppm source

10.7% total NO breakthrough for the entire 121 minutes

Several other experiments were carried out:

• To evaluate the impacts of temperature on the NOx storage equilibruim (i.e. storage capacity)

• Variations of chemistry in production of the absorbent (e.g. Barium/Cobalt)

• Regeneration of the coated GROG

• Optimal depth of the CO-GROG, and the impacts on removal/storage capacity

Temperature Variance Exp.

Temp. Ramp NO Desorb Experiment

0

50

100

150

200

250

0 15 30 45 60 75 90 105 120

Time (Minutes)

FT

IR R

es

po

ns

e (

PP

M)

50C

100C125oC

150C

175C

The Depth Chamber Experiment

Campaign #3May/June 2006

The Scale up of the mini-denuder experiments !

Due to lack of time and resources, no experimentation was performed on the new denuder

prior to the field campaign

The New Denuder

Some Specs.

• 66” length (packed section) x 14.5” (internal diameter) was constructed in the spring of 2006

• internal 57-channel configuration, with perforated tubing

• The cylindrical channels have a 1” O.D., with an appropriate external spacing (between channels) for the optimal NOx absorbent performance (established via depth experiments).

Shipping to Spain

Assembly

Run type NOx Denuder usage

Engine-out NOx(ppm)

Time of DE injection (min)

Chamber NOx (ppm)

DPM (μg/m3)

Median diameter (nm)

Mean diameter (nm)

DE, dark No 430 6 1.7 33 62 71

DE, dark No 410 10 2.6 60 61 69

DE, dark Yes 390 20 0.009 30 75 84

DE, light Yes 415 27 0.050 54 88 100

DE, light+OH Yes 400 15+10+10* 0.025 37 87 96

DE, light+OH Yes 410 17+7+6* 0.025 30 91 100

DE, light Yes 371 20+10** 0.024 42 94 103

DE, light +toluene

Yes 363 20+10** 0.034 39 93 102

DE, dark No - 10 2.5 66 65 74

Some initial results

Another example of denudation-based sampling method.

• Capture of semi-volatile organic compounds (SVOC) on a glass annular denuder

XAD Denuder

Gundel et al., Atmos. Environ., 1995

Gundel and Lane, 1999

Denuder

Gas phase and particles with adsorbed SVOC enter an annular diffusion denuder

Filter

Solid Adsorbent

Gas phase molecules diffuse to, are trapped on, and retained by the denuder walls

Because the particles have much greater momentum than gas phase molecules, they pass through the denuder and are trapped on a filter

Some of the particle-associated SVOC leave the particles and are trapped on the solid adsorbent

Chemical extractionand analysis of thedenuder yields the

The sum on the filter and the solid adsorbentyields the

Annular Diffusion DenuderAnnular Diffusion Denuder

Doug Lane, Organic Speciation Workshop, Las Vegas, NV, 2004

• MICROSCOPIC CREVICES IN RESIN BEADS TRAP GAS MOLECULES WHEN THEY HIT THE WALLS OF THE INTEGRATED ORGANIC VAPOR/ PARTICLE SAMPLER.

From: Preuss, P. Berkeley Lab: Science Beat, Sept 1, 1999.

Operational Definitions of SVOC and PM - Associated OC

Filter-Adsorbent (FA) AF

AFDDenuder-Filter-Adsorbent (DFA)

AEElectrostatic precipitator (EA)

Filter-Filter-Adsorbent (FFA)

F1F A

Lara Gundel, Organic Speciation Workshop, Las Vegas, NV, 2004

Problems with Denuders

• XAD-4 denuders are difficult to use and labor intensive

• Denuders that adsorb gases can act as chromatographic columns

• Particles that are less than 50 nm behave more like gases than particles in a denuder

• Longer denuders are more effective gas traps, but increased transit time results in larger particle losses and a greater chance for particle-associated molecules to leave the particle while it passes through the denuder

• Learning to balance the trade-offs is a necessary skill for interpreting and successfully using denuder technology

From: “Challenges in Speciation of Aerosols”, by B. Zielinska

Particle Size and number distribution for

dark diesel exhaust aging in EUPHORE, 2006

Particle Size distribution Chamber B

0

50000

100000

150000

200000

250000

0 50 100 150 200 250 300Dp (nm)

dN

/dL

og

Dp

(#/

cm3

)

11:40:59

13:20:57

18:15:50

13-Jun-2006

D-1 run in June 2006

Particle Size and # distribution for dark

diesel exhaust aging with NOx denuder, 2006

Particle Size distribution Chamber B

0

10000

20000

30000

40000

50000

60000

70000

0 50 100 150 200 250 300

Dp (nm)

dN

/dL

og

Dp

(#

/cm3)

14:27:40

16:07:38

18:07:35

31-May-06

SMPS data displays a D-1 experiment in May 2006, with the NOx denuder connected

Discussion

• The initial mean and median particle diameter increased to ~90nm, with the denuder in-line

• The required increase in diesel exhaust injection time to the chamber when utilizing the denuder may explain this shift (i.e. more time for the small particles to coagulate, or residence time).

• 50nm particles begin to act like gases (i.e. diffusivity coefficient)

Additional Analyses

• Polyaromatic Hydrocarbons (PAH)

• Nitrated-PAH (NPAH)

• Polar compounds

• Alkanes, Hopanes, Steranes (fuel combustion markers)

Thank Our Sponsor

The Health Effect Institute

www.healtheffects.org

The Health Effects Institute"A Partnership of the U.S. Environmental Protection Agency and Industry"

Contact me for further information:

• Email: ssamy@dri.edu

• Phone: 674-7095

• Future Projects, Questions, Comments.